The present invention relates to intraocular lenses which are implanted in the eye to correct ametropia.
A phakic refractive lens (PRL) is surgically implanted inside the eye for correcting ametropia, particularly myopia and hyperopia. PRLs can be divided into two classes: anterior chamber PRLs and posterior chamber PRLs. An anterior chamber PRL (1) is positioned behind the cornea (2) and in front of the iris (3) while a posterior chamber PRL is behind the iris (3) and in front of the human natural crystalline lens (4) (FIG. 1). The PRL is the only reversible procedure for correcting severe refractive errors for both myopic and hyperopic patients.
There are two classes of materials that can be used for making PRLs: hydrophilic and hydrophobic materials. Although hydrophilic materials have been recently used for PRLs or intraocular lenses, their long term biocompatibility still needs to be established. On the other hand, hydrophobic materials, such as silicone and acrylic, have been used for PRLs and intraocular lenses after cataract surgery for more than a decade. These hydrophobic materials have been long established in terms of biocompatibility and are well tolerated by human eyes.
Nevertheless, when hydrophobic materials such as silicone are used to make a PRL having a floating lens design, there is a problem which needs to be solved: the silicone PRL does not submerge into an aqueous medium due to its extremely hydrophobic surface properties. The surface hydrophobicity keeps the PRL floating on the water surface instead of in water. This repelling force of the PRL from water is undesirable because the inside of the eye, whether in the anterior chamber or in the posterior chamber, is full of an aqueous liquid, i.e., the aqueous humor. The PRL needs to be surrounded with aqueous humor and its surface needs to be compatible with aqueous humor.
The present invention utilizes a number of methods that can change the PRL surface properties so that it can float submerged in an aqueous medium. Modification of the len""s surface properties solves the problem of incompatibility of a hydrophobic PRL with the aqueous humor of the eye.
U.S. Pat. No. 4,585,456, Blackmore, issued Apr. 29, 1986, discloses a phakic intraocular lens (IOL) composed of flexible materials which is positioned against the natural lens of the eye and held in place immediately adjacent to the natural lens and the ciliary sulcus. There is no disclosure of how the phakic IOL avoids complications, such as cataract formation, or methods used for preparation of the disclosed phakic IOL.
U.S. Pat. No. 5,480,428, Federov, issued Jan. 2, 1996, discloses a novel phakic lens design which has an opening at the center of the optic body. This opening is said to allow aqueous humor to flow through the lens body, thereby preventing intra-ocular pressure (IOP) elevation, but it also reduces the optical performance of the lens. Furthermore, this patent does not disclose the method for preparation of the disclosed phakic IOL. Fedorov, in U.S. Pat. No. 5,258,025, discloses that post-operative inflammation, caused by the contact of the supporting elements of the phakic IOL with the ocular tissue, is prevented by moving supporting elements to the periphery of the phakic lens. The Zinn""s zonules are thought to be strong enough to hold the supporting elements in place without causing inflammation. Thus, this patent teaches a PRL which is permanently fixed into the zonules of the eye, also called a sulcus fixation PRL. Lastly, PCT Published Application WO 98/17205, Valunin et al., published Apr. 30, 1998, describes the structure of a phakic IOL which is not fixed in the eye. Whether the disclosed lens has the ability to float submerged in water, rather than on its surface, and the surface treatment of the phakic IOL are not disclosed or discussed.
Worst, in his U.S. Pat. No. 5,192,319, issued Mar. 9, 1993, discloses an anterior chamber PRL design for correcting ametropia. No methods of preparation for such anterior chamber lenses are disclosed. Baikoff, in his U.S. Pat. No. 5,300,117, issued Apr. 5, 1994, describes another anterior chamber PRL design for correcting myopia. No methods for preparation of the lens are disclosed.
Yang, et al, in U.S. Pat. No. 5,397,848, issued Mar. 14, 1995, discloses a chemical method for enhancing the hydrophobicity of silicone polymers by introducing a hydrophilic component into the crosslinked silicone polymer networks.
Fedorov, in Russian Patent RU (11) 2032544 (1989), discloses that the use of vacuum UV in the production of ophthalmic lenses can shorten production time, and increase yields and lens biocompatibility. Specifically, lenses after application of the vacuum UV process are taught to be more resistant to the damage caused by lasers. The improvement in laser resistance is important because after cataract surgery and IOL implantation approximately 30% of the patients will develop secondary cataracts. The treatment for the secondary cataract formation utilizes a YAG laser. Therefore, IOLs need to be laser resistant. However, there is no discussion of modifying the surface energy of a PRL made from hydrophobic materials so that it can float submerged in an aqueous medium, instead of on the surface of the aqueous medium.
Vacuum ultraviolet irradiation has also been applied to silicones for improvement of micro-wear resistance (V. N. Vasilets, et al., Polymer, 39 (13): 2875-2881 (1997)). Micro-wear resistance and gamma radiation resistance are critical for equipment used in outer space exploration. Vacuum UV is one of the technologies used for improvement of surface wear. It is also known that vacuum UV will change the chemical structure, especially the surface structure of silicone materials. (See, for example, L. S. Chabrova, et al., C-MRS Int. Symp. Proc. 1991, Meeting Date 1990, Vol. 3, 505-508).
Other surface activation techniques are also well-known for various applications. For example, U.S. Pat. No. 5,147,397, Christ, issued Sep. 15, 1992, discloses the use of a plasma treatment to enhance the bondability of the haptics to the optic portion of a lens. In another example, U.S. Pat. No. 5,603,774, LeBeouf, issued Feb. 18, 1997, discloses that the tackiness associated with soft acrylic polymers can be reduced by plasma treatment of the polymer surface. In this example, plasma surface modification is used to change adhesion properties of the lens, not the hydrophilicity/hydrophobicity of the lens surface.
U.S. Pat. No. 4,573,998 (issued Mar. 4, 1986) and U.S. Pat. No. 4,702,244 (issued Oct. 27, 1987), both by Mazzocco, disclose an improved intraocular lens structure comprising a deformable optical zone portion, which enables surgeons to deform the lens, such as folding, compression, rolling, stretching, etc., so that the lens can be implanted through a smaller incision. The small incision has been shown to provide benefits to patients, such as less trauma, fast recovery and less induced astigmatism.
It is an object of the present invention to provide a PRL, with proper lens design and properties, that can be placed inside the human eye for correction of refractive errors. It is also an object of this invention that this PRL can float submerged in the aqueous humor and that the PRL be very flexible and soft. More specifically, an object of the present invention is to provide methods for modifying surface properties of a hydrophobic PRL so that it can float submerged in an aqueous medium. This capability of a hydrophobic PRL to float submerged in an aqueous medium is critical because the inside of the eye contains aqueous humor, which is an aqueous material.
These and other objects may be accomplished using a method for surface treatment of a phakic refractive lens made from hydrophobic materials (such as silicone materials) so that the treated lens can float submerged in an aqueous medium, said method comprising the steps of:
(a) testing the hydrophobic lens in an aqueous medium to ascertain whether the lens can float submerged in the aqueous medium; if the untreated lens can only float on the surface of the aqueous medium instead of floating submerged in the aqueous medium, then
(b) performing a surface treatment process on the lens, such as one to make the surface of the lens more wettable (preferably less hydrophobic), for example, the vacuum UV process or the corona discharge process.
The present invention also relates to a phakic refractive lens made from a hydrophobic material which floats submerged when placed in an aqueous medium.